1. Field of the Invention
The present invention is directed to a system and method for suppressing fires in normally occupied areas utilizing non-azide solid propellant inert gas generators. In one aspect, this invention relates to the use of solid propellant inert gas generators for suppressing fires in occupied spaces whereby human life can still be supported in those spaces for a period of time.
2. Description of the Related Art
Numerous systems and methods for extinguishing fires in a building have been developed. Historically, the most common method of fire suppression has been the use of sprinkler systems to spray water into a building for cooling the fire and wetting additional fuel that the fire requires to propagate. One problem with this approach is the damage that is caused by the water to the contents of the occupied space.
Another method is the dispersal of gases, such as nitrogen, to displace oxygen in an enclosed space and thereby terminate a fire while still rendering the enclosed space safe for human occupancy for a period of time. For example, U.S. Pat. No. 4,601,344, issued to The Secretary of the Navy, discloses a method of using a glycidyl azide polymer composition and a high nitrogen solid additive to generate nitrogen gas for use in suppressing fires. The problem with the method disclosed in U.S. Pat. No. 4,601,344 is that azide compositions are used, which potentially may be harmful to human health and which typically generate less gas by weight relative to non-azide compositions.
Yet another method is the dispersal of gases, such as Halon 1301, to chemically suppress a fire. These systems store the Halon 1301 gas in a liquid state under pressure in compressed gas cylinders. Typically, a plurality of such cylinders is required for a single small building. The use and maintenance of compressed gas cylinders is expensive. Further, they are often stored in a separate location in the building, thereby detracting from the usable floor space in a building.
Due to their use of ozone depleting greenhouse gases, Halon 1301 systems are being replaced by more environmentally friendly alternative systems, as mandated by the 1987 Montreal and 1997 Kyoto International Protocols. One example of a Halon 1301 alternative system uses HFC (e.g. FM-200 Fire Suppression System manufactured by Kidde Fire Systems), while others use an inert gas mixture (e.g. Inergen Fire Suppression System manufactured by Ansul Incorporated, or the system set forth in U.S. Pat. No. 4,807,706 issued to Air Products and Chemicals Inc.)
One disadvantage of such Halon 1301 alternate systems, is that they require substantially more fire suppression agent/gas on a lb per lb ratio than Halon 1301 (and therefore even more compressed gas cylinders) to produce the same performance. These new Halon 1301 alternative systems also require the use of high pressure piping and nozzle delivery systems to transport the agent to the protected area. This increases the cost of the system.
The existing ubiquitous Halon 1301 systems are used in North America for asset protection in high risk areas, such as electrical transformer vaults, airport control towers, computer rooms, telephone switch gear enclosures, etc., which operate 24 hours per day. In order to install a Halon 1301 alternative system which, as indicated above, uses discharge piping and nozzles, requires the end user of these systems to shut down the equipment (i.e. assets) being protected in order to install the alternative system. Such shut down procedures can be expensive.
U.S. Pat. Nos. 6,016,874 and 6,257,341 (Bennett) disclose the use of a dischargeable container having self-contained therein an inert gas composition. A discharge valve controls the flow of the gas composition from the closed container into a conduit. A solid propellant is ignited by an electric squib and burns thereby generating nitrogen gas. The propellant is said to be a mixture of sodium azide and sulphur which, as indicated above, can be harmful to human health.
Non-azide solid propellants are known in the art for inflating air bags and actuating seatbelt pretensioners in passenger-restraint devices, such as described in U.S. Pat. Nos. 5,520,826 (Reed Jr. et al) and 6,287,400 (Burns et al). However, there is no discussion in the art of using non-azide compositions in a system, which does not contain any compressed gas containers and piping, for extinguishing fires in normally occupied spaces.